Surveys of American voters released this week show Republican presidential nominee Donald Trump trailing his Democratic opponent, Hillary Clinton, by a fairly wide margin following last month's Democratic National Convention.

The most recent survey, a McClatchy-Marist poll, shows Clinton leading Trump by a margin of 48 percent to 33 percent. The same survey last month showed Clinton with a much smaller edge — 42 percent to 39 percent — over her Republican challenger.

The director of the Marist College polling group, Lee Miringoff, said Friday that the rapid switch in voters' preferences shows "a Trump candidacy in jeopardy."

The poll was conducted Monday through Wednesday of this week and was released late Thursday. Miringoff said "a long list of unforced errors by Trump" — including the controversy generated by his criticism of a Muslim couple who spoke at the final session of the Democratic convention on July 28 — and a "post-convention bounce" in support for Clinton accounted for the poll results.

Not all the numbers, however, are positive for former Secretary of State Clinton. The Marist poll indicated 40 percent of registered voters said the main factor that prompted them to support Clinton was their opposition to Trump.

The poll said 55 percent of registered voters have an unfavorable opinion of Clinton. However, Trump is worse off, with 66 percent of those surveyed declaring they have an unfavorable opinion of the billionaire businessman.

When it comes to voters under 30, opinions are clear.

Both the McClatchy poll and a survey of voters conducted by GenForward show less than 25 percent of voters aged 18 to 30 have a favorable opinion of Trump.

Within this group, the McClatchy poll showed 23 percent would vote for third-party Libertarian candidate Gary Johnson, although the GenForward poll said seven out of 10 young voters don't feel they know enough about Johnson to vote for him.

Green Party candidate Jill Stein saw similar support, with 16 percent saying they would vote for her, according to the McClatchy-Marist survey.

Democratic presidential candidate Hillary Clinton speaks at the 2016 National Association of Black Journalists' and National Association of Hispanic Journalists' Hall of Fame Luncheon at Marriott Wardman Park in Washington, Aug. 5, 2016.

Clinton still faces distrust and dislike from voters of all age ranges in light of a scandal surrounding her use of a private email server at her home to conduct government business. When asked about her likability in a question-and-answer session at a Washington conference for minority journalists Friday, she cited her approval ratings as secretary of state when she left office — 66 percent — and said she was confident that when voters truly listened to her platform, they would support it.

"I'm going to go up there and make my case. … People will hear it," she told the convention.

GenForward is a survey by the Black Youth Project at the University of Chicago, in conjunction with the Associated Press-NORC Center for Public Affairs Research. It is designed to pay special attention to the voices of nonwhite young adults, highlighting how race and ethnicity shape the opinions of a new generation.

The survey results presented Friday were based on interviews conducted between July 9 and July 20.